This invention is directed to radiography in which radiation is aimed at certain regions of a subject to provide therapy treatment. In particular, it is directed to an asymmetric contrast radiographic portal imaging assembly containing a combination of radiographic silver halide films and to methods of use. This invention is useful in portal radiography.
In conventional medical diagnostic imaging the object is to obtain an image of a patient""s internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) and U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Kelly et al.), U.S. Pat. No. 4,900,652 (Kelly et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and Research Disclosure, Vol. 184, August 1979, Item 18431.
Radiation oncology is a field of radiology relating to the treatment of cancers using high energy X-radiation. This treatment is also known as teletherapy, using powerful, high energy X-radiation machines (often linear accelerators) to exposure the cancerous tissues (tumor). The goal of such treatment is to cure the patient by selectively killing the cancer while minimizing damage to surrounding healthy tissues.
Such treatment is commonly carried out using high energy X-radiation, 4 to 25 MVp. The X-radiation beams are very carefully mapped for intensity and energy. The patient is carefully imaged using a conventional diagnostic X-radiation unit, a CT scanner, and/or an MRI scanner to accurately locate the various tissues (healthy and cancerous) in the patient. With full knowledge of the treatment beam and the patient""s anatomy, a dosimetrist determines where and for how long the treatment X-radiation will be directed, and predicts the radiation dose to the patient.
Usually, this treatment causes some healthy tissues to be overexposed. To reduce this effect, the dosimetrist provides one or more custom-designed xe2x80x9cblocksxe2x80x9d or shields of lead around the patient""s body to absorb X-radiation that would impact healthy tissues.
To determine and document that a treatment radiation beam is accurately aimed and is effectively killing the cancerous tissues, two types of imaging are carried out during the course of the treatment. xe2x80x9cPortal radiographyxe2x80x9d is generally the term used to describe such imaging. The first type of portal imaging is known as xe2x80x9clocalizationxe2x80x9d imaging in which the portal radiographic film is briefly exposed to the X-radiation passing through the patient with the lead shields removed and then with the lead shields in place. Exposure without the lead shields provides a faint image of anatomical features that can be used as orientation references near the targeted feature while the exposure with the lead shields superimposes a second image of the port area. This process insures that the lead shields are in the correct location relative to the patient""s healthy tissues. Both exposures are made using a fraction of the total treatment dose, usually 1 to 4 monitor units out of a total dose of 45-150 monitor units. Thus, the patient receives less than 20 RAD""s of radiation.
If the patient and lead shields are accurately positioned relative to each other, the therapy treatment is carried out using a killing dose of X-radiation administered through the port. The patient typically receives from 50 to 300 RAD""s during this treatment. Since any movement of the patient during exposure can reduce treatment effectiveness, it is important to minimize the time required to process the imaged films.
A second, less common form of portal radiography is known as xe2x80x9cverificationxe2x80x9d imaging to verify the location of the cell-killing exposure. The purpose of this imaging is to record enough anatomical information to confirm that the cell-killing exposure was properly aligned with the targeted tissue. The imaging film/cassette assembly is kept in place behind the patient for the full duration of the treatment. Verification films have only a single field (the lead shields are in place) and are generally imaged at intervals during the treatment regime that may last for weeks. Thus, it is important to insure that proper targeted tissue and only that tissue is exposed to the high level radiation because the levels of radiation are borderline lethal.
Portal radiographic imaging film, assembly and methods are described, for example, in U.S. Pat. No. 5,871,892 (Dickerson et al.) in which the same type of radiographic element can be used for both localization and portal imaging.
Portal imaging assemblies can be grouped into two categories. The first type of assemblies includes one or two metal plates and a radiographic silver halide film that is designed for direct exposure to X-radiation. Two such films that are commercially available are KODAK X-ray Therapy Localization (XTL) Film and KODAK X-ray Therapy Verification (XV) Film. Each of these films is generally used with a single copper or lead plate. They have the advantage of having low contrast so that a wide range of exposure conditions can be used to produce useful images. However, because high energy X-radiation is used to produce therapy portal images, the contrast of the imaged tissues (target tissues) is also very low. Coupled with the low contrast of the imaging system, the final image contrast is very low and difficult to read accurately.
The second type of portal imaging assemblies includes a fluorescent intensifying screen and a silver halide radiographic film. These assemblies include one or two metal plates, one or two fluorescent intensifying screens, and a fine grain emulsion film. Because a significant amount of the film""s exposure comes from the light emitted by the fluorescent screen(s), it is possible to use films that provide high contrast images. Thus, these imaging assemblies typically provide images having contrast 3.5 times higher than those direct imaging assemblies noted above do. However, the photospeed obtained with both types of assemblies is about the same.
Problem to be Solved
However, the imaging assemblies of the prior art present some problems. Due to their high contrast images and the variations in patient treatment dosages, patient tissue conditions (thickness), and exposing equipment, it is more difficult to obtain correct exposures. The images are either too light or too dark. Exposure can be controlled by adjusting the so-called xe2x80x9cair gapxe2x80x9d distance and monitor setting between the patient and the imaging system. Unfortunately, many therapy machines used in therapy imaging (especially therapy verification imaging) do not allow for an adjustable xe2x80x9cair gapxe2x80x9d. This is especially true for therapy verification imaging.
Thus, there is a continuing need in the health imaging industry to provide a highly effective means for portal imaging under a wide variety of exposure conditions. More particularly, there is a need for portal imaging assemblies that provide greater xe2x80x9cexposure latitudexe2x80x9d without loss of photospeed or contrast. The present invention is directed to solving these problems.
This invention provides a solution to the noted problems with a radiographic imaging assembly comprising a high contrast first radiographic silver halide film arranged in association with a lower contrast second radiographic silver halide film, the first and second radiographic silver halide films optionally further arranged in association with one or more fluorescent intensifying screens,
(a) the first radiographic silver halide film comprising a support having first and second major surfaces and is capable of transmitting X-radiation,
the first radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer,
each of the silver halide emulsion layers comprising silver halide cubic grains that have the same or different composition in each silver halide emulsion layer, and all hydrophilic layers of the first radiographic silver halide film being fully forehardened and wet processing solution permeable for image formation within 45 seconds,
(b) the second radiographic silver halide film comprising a support having first and second major surfaces and is capable of transmitting X-radiation,
the second radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer,
each of the silver halide emulsion layers comprising silver halide cubic grains that have the same or different composition in each silver halide emulsion layer, and all hydrophilic layers of the second radiographic silver halide film being fully forehardened and wet processing solution permeable for image formation within 45 seconds, and
wherein the ratio of the contrast of the first radiographic silver halide film to the contrast of the second radiographic silver halide film is at least 1.25.
Further, this invention provides a method of providing a black-and-white image comprising exposing the radiographic imaging assembly described above, and processing the first and second radiographic silver halide films, sequentially, with a black-and-white developing composition and a fixing composition, the processing being carried out within 90 seconds, dry-to-dry.
Still again, this invention provides a method of confirming the targeting of X-radiation comprising:
A) directing the X-radiation at a region of a subject containing features that are identifiable by differing levels of X-radiation absorption and creating a first image of X-radiation penetrating the subject with the radiographic imaging assembly described above wherein the X-radiation is directed to pass through the one of the radiographic silver halide films before it is passed through the other radiographic silver halide film,
B) directing X-radiation at the region of the subject and creating a second image superimposed on the first image in the first exposed radiographic silver halide film,
C) processing the first and second radiographic films of the radiographic imaging assembly to obtain a viewable image from which intended targeting of the X-radiation directed at the region in relation to the identifiable features of the subject is realized,
wherein during steps A and B, total X-radiation exposure is limited to 10 seconds or less, at least one metal screen capable of emitting electrons when exposed to X-radiation is interposed between the source of X-radiation and the first exposed radiographic silver halide film, and at least one fluorescent intensifying screen is positioned to receive electrons from the metal screen and to emit light to expose the first exposed radiographic silver halide film.
The present invention provides a means for providing high contrast images in portal imaging using a wide variety of therapy imaging machines under a wide variety of conditions. Thus, the present invention provided improved xe2x80x9cexposure latitudexe2x80x9d and xe2x80x9cdynamic rangexe2x80x9d in this important field of radiology. In addition, the radiographic imaging assembly (first and second films and optional intensifying screen) of this invention may provide improved image tone in the films and greater processing uniformity (less processing defects). In addition, all other desirable sensitometric properties are maintained and the first and second films can be rapidly processed in the same conventional processing equipment and compositions.
These advantages are achieved by using two radiographic silver halide films in combination, which films provide images with different contrasts from the same imaging X-radiation. That is, the ratio of the contrast of an image provided by the first (higher contrast) film to the contrast of an image provided by the second (lower contrast) film is at least 1.25, and preferably at least 1.75, and more preferably from about 2 to about 2.5. These films are arranged xe2x80x9cin associationxe2x80x9d that means they are generally in physical contact with no significant gap between them in the imaging assembly.
Imaging X-radiation can be directed first through either of the two radiographic silver halide films in the imaging assembly before it passes through the other radiographic silver halide film in the imaging assembly. Preferably, one or more intensifying screens are included in the radiographic imaging assembly and are arranged as described below.